Luminescence properties and Crystal structures of Pr-doped GPS

Crystal structures and scintillation properties of praseodymium-doped gadolinium pyrosilicate (Gd2Si2O7:Pr, GPS:Pr) were investigated as a part of systematic studies of a Gd2Si2O7 system as scintillation materials. Transparent yellowish-green polycrystalline GPS:Pr was grown using the floating zone growth method. The crystal structure, which is strongly related with the mean ionic radius of rare-earth elements, was orthorhombic with Pna21 space group for 5 and 10 mol% Pr concentration. It was triclinic with P/1 space group for 15 mol% and 20 mol% Pr concentration. A fluorescence spectrum was composed of a peak located at 300 nm and a broad peak around 360 nm. Light yield of ca. 80% of a GSO:Ce scintillator was confirmed with GPS:Pr (Pr=10 mol%) for 662 keV gamma rays; the decay time was 26 ns. Unexpectedly, GPS:Pr with a triclinic structure, i.e. Pr=15 and 20 mol%, showed no scintillation for gamma rays.